LTE model atmospheres with new opacities

Abstract

We describe an opacity sampled version of the LTE model atmosphere code sterne with revised continuous opacities. In particular, we examine the results of replacing the existing treatment of the continuous opacities which followed the method of Kurucz (1970, SAOSR, No. 309) and Peach (1970, MNRAS, 73, 1), with photoionization cross-sections from the Opacity Project and the IRON Project, and the effects of substituting an opacity distribution function method for treating the line opacities with an opacity sampling method. In studying the application of these new models to atmospheres with hydrogen-rich and extreme chemical compositions, we find the new opacity treatment increases the temperature in the line forming region by up to 3000 K for extremely hydrogen-poor stars and up to 1250 K for hydrogen-rich stars with T eff = 30 000 K and log g = 3.00. This translates into systematically cooler effective temperature measurements for these types of stars.

HST spectroscopy of chemically peculiar hot subdwarfs: PG 0909+276 and UVO0512–08

“…This was used to fit the basic parameters for each star ( Table 2). The package used for computing model atmospheres and theoretical spectra and for fitting these to the observations is - (Jeffery 2003;Winter 2006), which includes (Behara & Jeffery 2006), (Jeffery et al 2001a), _ (Jeffery 1991) and (Jef- ). These assume that the atmosphere is semi-infinite, plane parallel, and in radiative, hydrostatic, and local thermodynamic equilibrium.…”

Radial-velocity measurements of the pulsating zirconium star: LS IV−14°116*

“…The formal error in the position of the parabola apex was adopted as representative of the velocity error. The observer's frame radial velocity of the template was obtained by cross-correlation with a theoretical spectrum computed for a hot subdwarf with atmospheric abundances of hydrogen and helium being 70% and 30% by number, solar abundances of other elements, effective temperature T eff = 32 000 K, surface gravity log g = 5.5 ( cm s −2 ), and microturbulent velocity vt = 5 km s −1 (Behara & Jeffery 2006). This is not a perfect match to the observed spectrum, but completely satisfactory for the purpose of velocity measurement by cross correlation.…”

“…We can simulate the observable light and amplitude ratios for non-radial modes of different radial degree ℓ and azimuthal number m using the surface codes bruce and kylie (Townsend 2003;Ramachandran et al 2004) and a grid of theoretical spectra for a composition appropriate to LS IV −14 • 116 (Behara & Jeffery 2006;Naslim et al 2011). Assuming effective temperature T eff = 36 000 K, surface gravity log g = 5.6( cm s −2 ) and equatorial rotation velocity veq = 2 km s −1 (Naslim et al 2011), and also assuming the adiabatic approximation, a polar radius of 0.2 R⊙ (implying a mass M ≈ 0.5 M⊙), inclination i = 80 • , pulsation period 1950 s and an arbitrary surface velocity amplitude, we can compute a time series of theoretical spectra for a given mode ℓ, m. These can be analysed in exactly the same way as the UVES spectra to give both the apparent velocity amplitude and, also, the apparent flux amplitude in a given wavelength region.…”

An abundance analysis of a chemically peculiar B star – JL 87

“…The model atmospheres were computed using the recently improved LTE code sterne (Behara & Jeffery 2006). The models assume plane-parallel geometry, hydrostatic and radiative equilibrium.…”

“…Given Napiwotzki's result, the bulk of the difference would appear to be due to the improved opacity treatment. Since we also use opacity-sampled LTE model atmospheres, with an improved treatment of the continuous opacities (Behara & Jeffery 2006), systematic errors due to the assumption of LTE are likely to be small.…”